Hydrocolloid-containing adhesive compositions have been known for many years.
One example of such compositions is disclosed in U.S. Pat. No. 3,339,549 by Chen. This hydrocolloid-containing adhesive composition comprises a rubber elastomer, such as polyisobutylene, and one or more water-soluble or water-swelling hydrocolloids, such as a powdery mixture of pectin, gelatin, and carboxymethyl cellulose.
In this hydrocolloid-containing adhesive composition, the rubber elastomer provides adhesion properties and the hydrocolloid powder particles function to absorb exudates from wounds or sweat.
Use of such hydrocolloid-containing adhesive compositions in bandages for skin ulcers, burns, and other exudative wounds is gradually arousing attention.
For example, an occlusive multilayered bandage comprising a polymer film impermeable to external water, an intermediate layer which is a semi-open-cell polymer foam layer provided on one side of the polymer film, and an adhesive layer formed on the intermediate layer is proposed in JP-A-58-190446. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) This multilayered bandage is characterized in that the adhesive layer consists essentially of a homogeneous blend of one or more pressure-sensitive adhesive materials which may contain, if required and necessary, one or more thermoplastic elastomers with one or more water-dispersible hydrocolloids which may contain, if required and necessary, one or more water-swelling flocculating reinforcements and/or one or more polymers having hydrating properties.
However, this hydrocolloid-containing adhesive composition layer has a drawback that when the dressing is applied to a wounded part of the body, the adhesive layer swells as it absorbs an exudate from the wound and other body fluids, and the adhesive layer finally suffers a separation between components. This means that the rubber elastomer (rubber-based adhesive) which has served to bond hydrocolloid particles together is dispersed and comes to be present as dispersed independent particles.
As a result of the decrease of the interaction between the components constituting the hydrocolloid-containing adhesive composition layer, not only the adhesive layer loses the shape retention property to allow part of the adhesive composition to flow out from the substrate, but also the adhesion of the adhesive layer decreases at the edge parts of the applied dressing. Thus, the dressing comes to be unable to perform its function as a dressing.
Although the above problem may be overcome by increasing the strength of the rubber-based adhesive, the use of a rubber-based adhesive having an increased strength in an adhesive layer of the above-described type may cause a problem that when the adhesive layer is contacted with an exudate from a wound and with other body fluids, the hydrocolloid particles cannot swell sufficiently and, hence, the adhesive layer has a poor absorbing capacity.
For the above reason, use of special hydrocolloids (polymers) having the property of absorbing water and/or swelling in water is being studied recently.
For example, JP-A-2-13463 proposes use of hydrocolloid particles comprising particles of a polycationic hydrocolloid and particles of a polyanionic hydrocolloid.
In the above JP-A, water-soluble chitosan salts such as chitosan maleate and chitosan glutarate are enumerated as examples of the polycationic hydrocolloid, and pectin, carboxymethyl cellulose, alginic acid salts, and the like are enumerated as examples of the polyanionic hydrocolloid.
In dressings using such polycationic and polyanionic hydrocolloid particles, the combining force among hydrocolloid particles may be improved to some degree due to the use of the two kinds of hydrocolloid particles. However, these dressings have drawbacks that the adhesion of the adhesive layer to the body becomes low upon absorption of an exudate or body fluids and that part of the hydrocolloid-containing adhesive composition dissolves in the absorbed fluids and flows out from the backing.